Conventionally, a communication system is known in which a user operates an image forming apparatus to access a service providing apparatus, and uses a service provided by the service providing apparatus through the image forming apparatus. For example, in a known system, when a user registers an image forming apparatus at a service providing apparatus through a PC, the service providing apparatus notifies the PC about authentication information. And, once the user inputs the authentication information in the image forming apparatus, the user can access the service providing apparatus by using the image forming apparatus.